1. Field of the Invention
The present invention generally relates to detection of organic and inorganic contaminants as well as natural dissolved constituents, and more particularly to the analysis of water supplies for the measurement and characterization of organic and inorganic contaminants or natural dissolved constituents therein. In particular, this invention relates to devices and methods for measuring cumulative dissolved solute (contaminant) fluxes and cumulative fluid fluxes in flow systems. The term flow systems as used herein includes, but is not limited to, saturated and variably saturated geologic and non-geologic media, such as (1) saturated and unsaturated fracture rock aquifers, where flow occurs both within fracture planes separating different matrix blocks as well as within the more or less permeable matrix blocks themselves, and (2) saturated and unsaturated sedimentary (porous) aquifers, where flow occurs through the intergranular space as well as through possible preferencial flow paths of elevated hydraulic conductivities. It is an essential feature of the invention that is can be applied in both simply or multiply screened observations wells as well as in unscreened boreholes. The present invention also allows for the determination of parameters such as fracture (or preferential flow path) locations, separations, inclinations, orientations of inclination and aperture (width).
2. Description of the Relevant Art
The presence of solutes in ground water supplies and other water resources can present significant pollution problems. A wide variety of organic and inorganic contaminants may be present in subsurface, water-bearing geologic formations, depending on how the overlying land under consideration has been used. For example, many different organic solvents and related compounds (e.g., non-halogenated and halogenated organic compounds) may exist in groundwater supplies beneath factory sites and other locations where extensive use of these chemicals has occurred over long time periods or accidental spills or inappropriate disposal have occurred. Of particular concern are halogenated (e.g., chlorinated) solvents including perchloroethene (PCE), trichloroethene (TCE), dichloroethane (DCA), vinyl chloride (VC), methylene chloride (MC), and others. However, in addition to halogenated solvents, a wide variety of other organic compounds shall be encompassed within the term “organic contaminants” as discussed below. Of equal concern are the presence of benzene, toluene, xylenes, and other constituents of petroleum-based fuels (e.g., jet fuel, gasoline, diesel fuel, and the like) in waste-bearing geologic formations underlying various transportation-related facilities. Examples of such facilities include gasoline stations, airports, military bases, and the like. Other types of contaminants include various pesticides and nutrients used in crop production or suburban lawns and gardens or golf courses as well as trace metals such as arsenic and chromium and the like used in industrial operations. At many sites, both organic and inorganic contaminants may be found as mixtures. A contaminant group designated as polyaromatic hydrocarbons (PAHs), such as naphthalene, phenanthene, anthracene, benzo-a-pyrene and others, are constituents of coal and/or tars and creosote found at former gas manufacturing sites and wood treating facilities. Natural dissolved constituents are typically present to different degrees in the groundwater and originate from the dissolution of naturally occurring elements in a system. They can include, but are not limited to, cations such as sodium, calcium, magnesium; anions such as cloride, sulfate, bicarbonate; or natural dissolved carbon. Knowledge of the presence of natural dissolved constituents can significantly contribute to a better understanding of the condition and behavior of a groundwater resource. Extreme levels of natural dissolved constituents can also lead to pollution problems; hereafter, the term contaminants as introduced above shall also encompass naturally dissolved constituents. Regardless of the particular contaminants of concern, the presence of these chemicals at or near subsurface or surface water supplies is a considerable public health concern and of ecological significance. Accordingly, the present invention shall not be restricted to the monitoring of any given organic or inorganic compounds.
Several methods have been used to analyze water quality. Of particular importance is the analysis of groundwater existing in aquifers for concentrations of organic waste products. The term “aquifer” as used herein describes a large water-bearing geologic formation that is capable of yielding sufficient water to satisfy a particular demand (e.g., drinking water or industrial uses or irrigation needs). Prior testing methods have involved the drilling of wells directly into the aquifer, followed by the placement or not of screening materials within the wells depending on the stability of the borehole wall (e.g., stable rock or loose sediments). For deep aquifers, dedicated submersible pumps are then positioned in each well to withdraw numerous water samples of delivery to the wellhead. For shallow aquifers, bailing the water or pumping from above ground can be used for sampling. Thereafter, the samples are analyzed to determine the type and concentration of organic contaminants in the collected water samples. Measurement of water levels (or pressure) in a network of wells enables estimation of average fluid fluxes, if the hydraulic conductivity of transmitting of the aquifer is known.
While the prior methods provided important information regarding the levels of contamination in the water supplies of concern, they did not allow for the estimation of contaminant fluxes and fluid flow fluxes. There is another technology (Passive Flux Meter) that we have developed which uses a permeable, sorptive unit intercepting water flow and solute transport, and which is capable of measuring both cumulative water and solute fluxes. However, this technology is not designed for applications in fracture flow systems for various reasons: (1) cross connections between fractures may occur disturbing the natural flow regime; (2) difficult installation and removal from unscreened boreholes due to common irregularities and instabilities in fracture rock borehole walls; (3) creation of cavities due to borehole irregularities that the existing technology cannot compensate for; and (4) more difficult or impossible detection of dye tracer marks to determine fracture parameters and flow direction. Also, the Passive Flux Meter technology is not optimal for observation wells with multiple screen intervals (in any type of aquifer), since cross connections between different horizons can distort the measurement. Furthermore, Pan lysimeters (free drainage samplers) and suction lysimeters have both been used to measure cumulative fluid and dissolved solute fluxes in porous media when the direction of flow is vertical; however these technologies are not suitable for applications in fracture rock aquifers neither for measuring horizontal fluxes.
Parameters of a fracture rock flow system (fracture locations, separations, inclinations, orientations of inclinations and fracture apertures), for example, can be determined with existing, well known, geophysical technologies. However, these methods are instrumentally cumbersome and do not provide measurements of water or solute fluxes. Thus, to simultaneously measure magnitudes and directions of cumulative fluid fluxes or cumulative solute fluxes associated with one or more fluids flowing in a fracture flow systems, and to simultaneously determine parameters such as fracture locations, separations, inclinations, orientations of inclinations and fracture apertures, a new method is needed.
Current methods for estimating contaminant mass flux (J) in aquifers are made from independent instantaneous measurements of flux (q0) and solute concentration (C) in the pore or fracture water. Several methods exist for measuring q0 and C in saturated and unsaturated geologic formations. All existing methods are confined to providing estimates characterized over vertical or horizontal sampling lengths. For example, in cases of horizontal saturated flow, q0 and C are estimated over isolated vertical segments of a well, whereas in estimating solute mass and fluid fluxes associated with vertical infiltration or leaching, the pertinent sampling lengths are the horizontal or areal extents of infiltration. Continuous temporal measurements of q0 can be done for saturated flow systems. Methods of measuring vertical unsaturated flow require that the flow be intercepted and then retained for direct volumetric measurement and chemical analysis. Thus, there is a method for estimating vertical cumulative water fluxes.
Solute concentrations (C) are usually measured at discrete moments in time in both saturated and unsaturated flow systems. However, a device exists to intercept vertical unsaturated flow. Chemical analysis of the water intercepted by this device could be used to estimate cumulative dissolved solutes transported as a result of vertical fluid flow. Measured q0 and C are used as shown in the following equation to estimate the instantaneous contaminant flux J.J=q0C  (1)Equation (1) is assumed to characterize contaminant mass flux over specified sampling dimensions (i.e., an isolated vertical segment of a monitoring well) and for a reported sampling time. For geologic media, this approach of characterizing contaminant fluxes is subject to significant experimental and conceptual errors. Consider first, that the specific discharge q0 (the magnitude and the direction) and solute concentration C are both functions of position and time. This suggests that the magnitude and the direction of mass flux J also vary with position and time. Thus, any sampling of q0 and C over an isolated vertical or horizontal length precludes accurate local estimation of the magnitude and the direction of both fluid and contaminant fluxes. Second, the short-term sampling procedures often used to obtain C and q0 preclude estimation of the time-integrated (i.e., cumulative) values for fluid and contaminant fluxes. Such time-integrated contaminant fluxes are useful for assessing health risks associated with groundwater contamination, for assessing the direction and mass flow of contamination leaving a compliance boundary, for assessing the total amount of off-site contamination contributed by one or more sources, and for assessing the benefits of removing or remediating sources of subsurface contamination. Finally, because the above equation uses spatially averaged values of q0 and C it does not produce valid estimates of contaminant fluxes in typically heterogeneous aquifers or vadose zone flow systems. Accurate estimates of length averaged contaminant fluxes are obtained only from the direct spatial integration of measured local contaminant fluxes J. Thus, existing methods for measuring q0 and C do not provide an adequate discrete or time integrated estimate of contaminant fluxes in saturated or variably saturated geologic formations with the exception of the Passive Flux Meter technology, which is capable of doing so, but yet, is not suited for applications in unscreened fracture rock observation boreholes and suboptimal for multiply screened monitoring wells.
Traditional testing methods for fracture rock borehole inspection also require a large amount of expensive equipment, are labor intensive, and involve complex operating procedures. Moreover, conventional monitoring techniques, which require the removal of numerous fluid samples for individual testing, typically generate large quantities of waste products (e.g., residual sample materials) that, if sufficiently contaminated, can present significant disposal problems. Prior to development of the present invention, a need therefore remained for an efficient testing system circumventing these disadvantages and enabling water supplies in aquifers to be tested in an accurate, rapid, and effective manner.
The claimed invention represents a unique and highly efficient alternative to the methods listed above, which claims to be applicable in both simply and multiply screened monitoring wells as well as unscreened observation boreholes. It does not require extensive equipment (e.g., submersible pumps) or complex operating procedures. The invented device can be used to analyze large water supplies without extracting any contaminated liquid sample materials so that problems with disposal of generated waste fluids are avoided. The invented device can be used to obtain continuous estimates of the magnitude and direction of both fluid and dissolved solute fluxes over one or more specified sampling intervals of different lengths including both flow in a number of fracture planes (or other types of preferential flow paths) and matrix flow inside a block (or flow through porous media in general) within a sampling interval. Sampling intervals can be defined by the lengths of screened intervals in a well casing or by arbitrary decision in the case of a continuous monitoring in an unscreened borehole. In the latter case, the device is furthermore capable of simultaneously indicating fracture plane locations, separations, inclinations, orientations of inclination and fracture apertures. Finally, the method and apparatus described below enable the water supply of interest to be simultaneously analyzed at multiple locations so that the contamination may be “mapped” enabling spatial delineation of the areas of concern. Decontamination of the water source can then occur in a more site-specific and accurate manner. The present invention therefore involves a highly effective testing system, which represents a substantial advance in the art of contaminant detection and remediation as discussed further below.